From 6cb356ca9fe063846cfb883ef484f7e7e411096c Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Tue, 3 Mar 2020 11:51:50 +0100 Subject: [PATCH 2/3] basic/fs-util: add a version of chmod_and_chown that doesn not use /proc --- src/basic/fs-util.c | 46 +++++++++++++++++++++++++++++++++++++++++ src/basic/fs-util.h | 1 + src/test/test-fs-util.c | 45 ++++++++++++++++++++++++++++++++++++++++ 3 files changed, 92 insertions(+) diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c index f8095e85d8..558cafbcaf 100644 --- a/src/basic/fs-util.c +++ b/src/basic/fs-util.c @@ -272,6 +272,52 @@ int fchmod_and_chown(int fd, mode_t mode, uid_t uid, gid_t gid) { return do_chown || do_chmod; } +int chmod_and_chown_unsafe(const char *path, mode_t mode, uid_t uid, gid_t gid) { + bool do_chown, do_chmod; + struct stat st; + + assert(path); + + /* Change ownership and access mode of the specified path, see description of fchmod_and_chown(). + * Should only be used on trusted paths. */ + + if (lstat(path, &st) < 0) + return -errno; + + do_chown = + (uid != UID_INVALID && st.st_uid != uid) || + (gid != GID_INVALID && st.st_gid != gid); + + do_chmod = + !S_ISLNK(st.st_mode) && /* chmod is not defined on symlinks */ + ((mode != MODE_INVALID && ((st.st_mode ^ mode) & 07777) != 0) || + do_chown); /* If we change ownership, make sure we reset the mode afterwards, since chown() + * modifies the access mode too */ + + if (mode == MODE_INVALID) + mode = st.st_mode; /* If we only shall do a chown(), save original mode, since chown() might break it. */ + else if ((mode & S_IFMT) != 0 && ((mode ^ st.st_mode) & S_IFMT) != 0) + return -EINVAL; /* insist on the right file type if it was specified */ + + if (do_chown && do_chmod) { + mode_t minimal = st.st_mode & mode; /* the subset of the old and the new mask */ + + if (((minimal ^ st.st_mode) & 07777) != 0) + if (chmod(path, minimal & 07777) < 0) + return -errno; + } + + if (do_chown) + if (lchown(path, uid, gid) < 0) + return -errno; + + if (do_chmod) + if (chmod(path, mode & 07777) < 0) + return -errno; + + return do_chown || do_chmod; +} + int fchmod_umask(int fd, mode_t m) { mode_t u; int r; diff --git a/src/basic/fs-util.h b/src/basic/fs-util.h index 78d68be9fd..6b9ade2ec1 100644 --- a/src/basic/fs-util.h +++ b/src/basic/fs-util.h @@ -34,6 +34,7 @@ int readlink_and_make_absolute(const char *p, char **r); int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid); int fchmod_and_chown(int fd, mode_t mode, uid_t uid, gid_t gid); +int chmod_and_chown_unsafe(const char *path, mode_t mode, uid_t uid, gid_t gid); int fchmod_umask(int fd, mode_t mode); int fchmod_opath(int fd, mode_t m); diff --git a/src/test/test-fs-util.c b/src/test/test-fs-util.c index d0c6fb82bf..d97ccfda3b 100644 --- a/src/test/test-fs-util.c +++ b/src/test/test-fs-util.c @@ -802,6 +802,50 @@ static void test_chmod_and_chown(void) { assert_se(S_ISLNK(st.st_mode)); } +static void test_chmod_and_chown_unsafe(void) { + _cleanup_(rm_rf_physical_and_freep) char *d = NULL; + _unused_ _cleanup_umask_ mode_t u = umask(0000); + struct stat st; + const char *p; + + if (geteuid() != 0) + return; + + log_info("/* %s */", __func__); + + assert_se(mkdtemp_malloc(NULL, &d) >= 0); + + p = strjoina(d, "/reg"); + assert_se(mknod(p, S_IFREG | 0123, 0) >= 0); + + assert_se(chmod_and_chown_unsafe(p, S_IFREG | 0321, 1, 2) >= 0); + assert_se(chmod_and_chown_unsafe(p, S_IFDIR | 0555, 3, 4) == -EINVAL); + + assert_se(lstat(p, &st) >= 0); + assert_se(S_ISREG(st.st_mode)); + assert_se((st.st_mode & 07777) == 0321); + + p = strjoina(d, "/dir"); + assert_se(mkdir(p, 0123) >= 0); + + assert_se(chmod_and_chown_unsafe(p, S_IFDIR | 0321, 1, 2) >= 0); + assert_se(chmod_and_chown_unsafe(p, S_IFREG | 0555, 3, 4) == -EINVAL); + + assert_se(lstat(p, &st) >= 0); + assert_se(S_ISDIR(st.st_mode)); + assert_se((st.st_mode & 07777) == 0321); + + p = strjoina(d, "/lnk"); + assert_se(symlink("idontexist", p) >= 0); + + assert_se(chmod_and_chown_unsafe(p, S_IFLNK | 0321, 1, 2) >= 0); + assert_se(chmod_and_chown_unsafe(p, S_IFREG | 0555, 3, 4) == -EINVAL); + assert_se(chmod_and_chown_unsafe(p, S_IFDIR | 0555, 3, 4) == -EINVAL); + + assert_se(lstat(p, &st) >= 0); + assert_se(S_ISLNK(st.st_mode)); +} + int main(int argc, char *argv[]) { test_setup_logging(LOG_INFO); @@ -819,6 +863,7 @@ int main(int argc, char *argv[]) { test_fsync_directory_of_file(); test_rename_noreplace(); test_chmod_and_chown(); + test_chmod_and_chown_unsafe(); return 0; }